Not always.
If they aren’t they’re sued into oblivion by some God hating parent in cahoots with the ACLU.
Would you like to see AGAIN the statistics showing grassroots support for teaching creation in public schools? I’d have to look it up but I know I have it available.
School boards that attempt to introduce creationism in school get voted out of office.
Moreover, once you decide to teach religious beliefs in public school; do you teach Mormonism in Utah, Islam in Michigan? How would that be determined?